1. Field of the Invention
The invention relates to Internet Protocol (IP) communication networks supporting hierarchical mobility management (i.e. comprising hierarchically organized points of presence (also known as home agents (HA)) and anchor points (also known as mobility anchor points (MAP))), and more precisely handover (call transfer) between access equipments of these networks involving at least one mobile (communication) equipment.
In the present context the expression “IP network” refers to a federation of subsets of IP networks (or IP subnetworks) interconnected by access equipments forming nodes, such as access routers.
In the present context, the expression “IP network using hierarchical mobility management” refers to an IP network in which calls between a mobile equipment (or node) and a communication equipment are effected via an agent equipment providing the home agent (HA) (or native) function for the mobile equipment, for example a home (or native) router, a mobility anchor point (MAP), for example a router, and a radio access equipment, for example an access router.
In the present context, the expression “mobile communication equipment” and the expression “mobile node” refer to any mobile (or portable) radio communication equipment (referred to hereinafter as a mobile equipment) capable of connecting to its home (sub)network (subnet) (or native subnetwork) or other subnetworks, referred to as remote (or external or foreign) subnetworks or visited networks, in order to exchange data in the form of signals with another communication equipment or with a subnetwork, for example, mobile telephones, laptop computers or personal digital assistants (PDA) equipped with a communication module.
2. Description of the Prior Art
Each mobile equipment that connects to an IP network has an IP home address (or IP native or permanent address) that corresponds to the prefix of the home (sub)network to which it is usually connected. When a mobile equipment is connected to its home network, data packets (or datagrams) sent to it are sent directly to its IP home address using a standard hop-by-hop type routing protocol. When the mobile equipment is roaming and wishes to connect to a remote (or external) subnetwork, it must configure itself with local and regional care-of (or complementary) addresses, known as care-of addresses, constructed from an address prefix supplied by the IP network, for example by means of a standard IPv6 mechanism, such as stateful or stateless autoconfiguration. These care-of addresses must be associated with the IP home address at the time of a binding update procedure effected between the mobile equipment and its home agent.
The person skilled in the art knows that there exist in the IP networks cited above IP mobility protocols, for example MIPv6, for ensuring that a mobile equipment can be contacted at any time and for ensuring the continuity of mobile equipment calls in progress, in particular during phases of transfer (handover) between access routers. Thus these protocols enable mobile equipments to maintain their connection to the Internet during handover and to continue to communicate with other equipments after changing their access (or attachment) point. However, they necessitate protocol operations and exchanges of signaling that introduce a phase during which the mobile equipment is no longer able to send or receive data packets (or datagrams).
A fast version FMIPv6 of MIPv6 has been proposed to limit the duration of this phase in which it is impossible to exchange packets, but only for handover between first and second access equipments connected to the same mobility anchor point, i.e. micromobility situations (in which mobility is limited to a single site (or anchor point) and is therefore characterized by local movements). It is therefore not applicable to handovers between first and second access equipments connected to first and second mobility anchor points, respectively, i.e. macromobility situations. Furthermore, FMIPv6 can only redirect a portion of the traffic which, on the one hand, does not limit sufficiently the duration of the phase in which it is impossible to exchange packets during a handover and, on the other hand, can lead to loss of packets.
Thus an object of the invention is to remedy the drawback cited above.